Functionalized ionic liquid electrolytes for lithium ion batteries

ABSTRACT

An ionic liquid that is a salt has a Formula: 
     
       
         
         
             
             
         
       
     
     Such ionic liquids may be used in electrolytes and in electrochemical cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/895,395, filed on Sep. 30, 2010, which is incorporated herein byreference, in its entirety, for any and all purposes.

STATEMENT OF GOVERNMENT RIGHTS

The United States Government has rights in this invention pursuant toContract No. DE-AC02-06CH11357 between the United States Government andUChicago Argonne, LLC, representing Argonne National Laboratory.

TECHNICAL FIELD

The present technology relates to ionic liquids, including roomtemperature ionic liquids, that may be used in electrolytes,electrolytic solutions and electrochemical devices. More particularly,the present technology relates to functionalized ionic liquids which areusable as electrolytes for lithium ion batteries having a high ionicconductivity, good solid electrolyte interphase (SEI) formation, highwettability, and high voltage stability.

BACKGROUND

Ionic liquids are substances, which are made up only from ions and havea melting point of <100° C. or are, ideally, liquid at ambienttemperature. They have been proposed for use in electrolytes for lithiumand lithium-ion batteries, as they exhibit relatively favorableelectrochemical stability and high ionic conductivity. Despite thepotential advantages, ionic liquids have not been widely used aselectrolytes for lithium and lithium ion batteries due to a number ofsignificant disadvantages. Although lithium-ion cells using LiMnO₂ andLi₄Ti₅O₁₂ as electrode materials show satisfactory cycling behaviorusing ionic liquid as electrolyte solvent, this cell configurationsuffers from the relatively small voltage of 2.5 V. In addition, thecell has low rate capability due to the high viscosity and poorwettability of the ionic liquid with electrode materials.

Moreover, early experiments to cycle lithium-ion batteries usingcarbonaceous negative electrode materials and ionic liquid-basedelectrolytes failed. Any ionic liquid sample tested was reduced at thelow potential at which the intercalation of lithium into the graphiteproceeds. It is believed that the reduction of the ionic liquidsproceeds due to the formation of dimeric species. For commercialapplications, lithium metal is, however, not advantageous. Due to thehigh reactivity of its surface, lithium is potentially hazardous,especially at elevated temperatures. Proposals to stabilize lithiatedgraphite electrodes for use in lithium-ion batteries include admixtureof small amounts of highly active film forming additives. Such additivescould protect against the continued reduction of the electrolyte itselfat the surface of the low potential graphite. However, in most cases,the additives have issues associated with the poor solubility in ionicliquid electrolytes.

SUMMARY

The present technology provides new ionic liquids for use inelectrolytes and electrochemical devices such as capacitors and lithiumion batteries. The ionic liquids bear functional groups so that shouldallow the ionic liquid itself to form passivation films on the surfaceof graphite-based anode materials and ensure stable cycling performance.The new ionic liquids also decrease the viscosity of the electrolytescompared to conventional ionic liquids, increasing their ionicconductivity; provide good electrode wettability by introducingsurfactant groups; and tolerate high potential, which reduces problemsrelated to the use of 4.8V transition metal oxides, especially againstovercharge. Finally, the ionic liquids of the present technology mayalso exhibit one or more of reduced flammability, thereby reducing therisk of burning and explosion in a misused battery; reduced vaporpressure, even at elevated temperatures; and are not environmentallyhazardous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B. ¹H-NMR oftriethyl-(methylenepentamethyldisiloxane)phosphonium iodide (IL1-I; FIG.1A) and triethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI, FIG. 1B).

FIGS. 2A and 2B. ¹H-NMR of 1-ethyl-3-(methylenepentamethyldisiloxane)imidazolium iodide (IL2-I, FIG. 2A) and1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide (IL2-TFSI, 2B).

FIGS. 3A and 3B. ¹H-NMR of1-ethyl-3-(ethylenemethylsulfone)-1H-imidazol-3-ium bromide (IL3-Br,FIG. 3A) and 1-ethyl-3-(ethylenemethylsulfone)-1H-imidazol-3-iumbis(trifluoro-methanesulfonyl)imide (IL3-TFSI, FIG. 3B).

FIG. 4. Li/MCMB half cell charge discharge profiles using conventional0.8M LiTFSI in tetraethylphosphonium bis(trifluoromethanesulfonyl)imideionic liquid.

FIG. 5. Li/MCMB half cell charge discharge profiles using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI).

FIG. 6. dQdV profile of Li/MCMB half cell using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI).

FIG. 7. LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li half cell charge dischargecycling performance using conventional 0.8M LiTFSI intetraethylphosphonium bis(trifluoromethanesulfonyl)imide ionic liquid.

FIG. 8. LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li half cell charge dischargecycling performance using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI) at 55° C.

FIG. 9. MCMB/Li half cell charge discharge cycling performance usingconventional 0.8M LiTFSI in tetraethylphosphoniumbis(trifluoromethanesulfonyl)imide ionic liquid.

FIG. 10. MCMB/Li half cell charge discharge cycling performance using0.8M LiTFSI in triethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI).

FIG. 11. MCMB/LiNi_(0.80)Ni_(0.15)Al_(0.05)O₂ full cell charge dischargecycling performance using conventional 0.8M LiTFSI intetraethylphosphonium bis(trifluoromethanesulfonyl)imide ionic liquid.

FIG. 12. MCMB/LiNi_(0.85)Co_(0.15)Al_(0.05)O₂ full cell charge dischargecycling performance using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI).

DETAILED DESCRIPTION

The following terms are used throughout as described below, unlesscontext clearly indicates otherwise.

Alkyl groups include straight chain and branched chain saturatedhydrocarbon groups having from 1 to 14 carbons unless indicatedotherwise. For example, a C₁₋₆ alkyl group includes alkyl groups with 1,2, 3, 4, 5, or 6 carbon atoms. In some embodiments, an alkyl group hasfrom 1 to 12 carbon atoms, from 1 to 10 carbons, from 1 to 8, 1 to 6, or1, 2, 3 or 4 carbon atoms. Examples of straight chain alkyl groupsinclude groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,n-hexyl, n-heptyl, and n-octyl, n-decyl, n-dodecyl and n-tetradecylgroups. Examples of branched chain alkyl groups include, but are notlimited to, isopropyl, iso-butyl, sec-butyl, tert-butyl, neopentyl,isopentyl, and 2,2-dimethylpropyl groups. Alkyl groups may beunsubstituted or are optionally substituted with one or more hydroxyl orhalogen groups.

Cycloalkyl groups include mono-, bi- or tricyclic alkyl groups havingfrom 3 to 12 carbon atoms in the ring(s), or, in some embodiments, 3 to10, 3 to 8, or 3, 4, 5, or 6 carbon atoms. Exemplary monocycliccycloalkyl groups include, but are not limited to, cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups.In some embodiments, the cycloalkyl group has 3 to 8 ring members,whereas in other embodiments the number of ring carbon atoms range from3 to 5, 3 to 6, or 3 to 7. Bi- and tricyclic ring systems include bothbridged cycloalkyl groups and fused rings, such as, but not limited to,adamantyl, decalinyl, and the like. Cycloalkyl groups may beunsubstituted or substituted as alkyl groups are.

Haloalkyl groups include alkyl groups as defined above in which 1 ormore of the hydrogen atoms are replaced by a halogen (i.e., F, Cl, Br,or I). In some embodiments the haloalkyl group bears from 1 to 3halogens. In others, the haloalkyl is perhalogenated such asperfluorinated or perchlorinated. Examples of haloalkyl groups includebut are not limited to —CH₂Cl, —CH₂F, —CF₃, —CH₂CH₂Br, and —CH₂CF₃.

Hydroxyalkyl groups are alkyl groups which bear at least one hydroxylgroup, i.e., OH. In some embodiments the hydroxyalkyl group bears 1 or 2hydroxyl groups.

Alkylene groups are alkyl groups, as defined herein, which are divalent;i.e., they have two points of attachment to a compound of the presenttechnology.

Aryl groups are cyclic aromatic hydrocarbons containing 6-14 carbonatoms and do not contain heteroatoms. Aryl groups herein includemonocyclic, bicyclic and tricyclic ring systems, including fused rings.Thus, aryl groups include, but are not limited to, phenyl, azulenyl,heptalenyl, biphenyl, fluorenyl, phenanthrenyl, anthracenyl, indenyl,indanyl, pentalenyl, and naphthyl groups. In some embodiments, arylgroups contain from 6-12 or even 6-10 carbon atoms in the ring portionsof the groups. In some embodiments, the aryl groups are phenyl ornaphthyl. Aryl groups may also include fused aromatic-aliphatic ringsystems, e.g., indanyl, tetrahydronaphthyl, and the like. Aryl groupsmay be unsubstituted or optionally substituted with one or more alkyl,halo groups or one or more halogens. In some embodiments the aryl groupsare substituted with 1, 2 or 3 alkyl groups and/or 1-5 halogens.

Aralkyl groups are alkyl groups as defined above in which a hydrogen orcarbon bond of an alkyl group is replaced with a bond to an aryl groupas defined above. In some embodiments, aralkyl groups contain 7 to 16carbon atoms, 7 to 14 carbon atoms, or 7 to 10 carbon atoms. Substitutedaralkyl groups may be substituted at the alkyl, the aryl or both thealkyl and aryl portions of the group. Representative aralkyl groupsinclude but are not limited to benzyl and phenethyl groups and fused(cycloalkylaryl)alkyl groups such as 4-indanylethyl. Aralkyl groups maybe unsubstituted or substituted. Representative substituted aralkylgroups may be substituted one or more times with alkyl groups orhalogens as for aryl and alkyl groups.

Heteroaryl groups are aromatic ring compounds containing 5 or more ringmembers, of which one or more is a heteroatom selected from N, O, S andP. Heteroaryl groups include, but are not limited to, groups such aspyrrolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl,thiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, thiophenyl,benzothiophenyl, furanyl, benzofuranyl, indolyl, azaindolyl(pyrrolopyridinyl), indazolyl, benzimidazolyl, imidazopyridinyl(azabenzimidazolyl), pyrazolopyridinyl, triazolopyridinyl,benzotriazolyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl,imidazopyridinyl, isoxazolopyridinyl, thianaphthyl, purinyl, xanthinyl,adeninyl, guaninyl, quinolinyl, isoquinolinyl, tetrahydroquinolinyl,quinoxalinyl, and quinazolinyl groups. Heteroaryl groups include fusedring compounds in which all rings are aromatic such as indolyl groupsand include fused ring compounds in which only one of the rings isaromatic, such as 2,3-dihydro indolyl groups. Heteroaryl groups may beunsubstituted or optionally substituted with one or more alky groups orone or more halogens. In some embodiments the aryl groups aresubstituted with 1, 2 or 3 alkyl groups and/or 1-5 halogens.

Heteroarylalkyl groups are alkyl groups as defined above in which ahydrogen or carbon bond of an alkyl group is replaced with a bond to aheteroaryl group as defined above. Representative heteroarylalkyl groupsinclude, but are not limited to, furan-2-yl-methyl,imidazol-4-yl-methyl, pyridin-3-yl-methyl, and indol-2-yl-propyl. Insome embodiments, the alkyl portion of the heteroarylalkyl group hasfrom 1 to 6 carbon atoms (i.e., 1, 2, 3, 4, 5, or 6). Heteroarylalkylgroups may be unsubstituted or substituted as heteroaryl and alkylgroups are.

A C₃₋₅ cyclic carbonate has from 3 to 5 carbon atoms in the ring,providing a 5 to 7 membered carbonate ring. Thus, for example, a C₃₋₅cyclic carbonate includes any of the following structures:

Aluminate is an aluminum oxide anion such as, but not limited to[Al_(x)O_(y)]⁻.

A halogen refers to any of fluorine, chlorine, bromine or iodine atoms.A halide is a halogen anion such as F, Cl⁻, Br⁻ or I⁻.

An isocyanate group has the chemical formula —N═C═O.

A maleic anhydride group (cis-butenedioic anhydride) has the structureshown below and may be attached to a compound at carbons 4 or 5.

An oxalic borate group is a boron anion to which one or two oxalategroups are bound. Oxalic borates thus include but are not limited to[B(C₂O₄)₂]⁻ and [F₂B(C₂O₄)]⁻. As part of a compound of formula I, theoxalic borate has a single oxalate group and may have a formula such as—[B(F)(C₂O₄)]⁻.

A succinic anhydride group has the structure shown below and may beattached to a compound at carbons 4 or 5.

A sulfate group has the chemical formula SO₄ ²⁻. Hence, alkyl sulfatesand aryl sulfates employed in the present technology are sulfatemonoesters of alkyl and aryl groups as defined herein. Thus alkyl andaryl sulfates include but are not limited to octyl sulfate, dodecylsulfate and the like.

Sulfolane is 2,3,4,5-tetrahydrothiophene-1,1-dioxide and may be attachedto a compound at any of carbons 2, 3, 4, or 5.

A sulfonate group has the chemical formula —SO₃ ⁻. Thus, alkylsulfonates are alkyl groups as defined herein bearing a sulfonate group,e.g., methyl sulfonate, ethyl sulfonate, dodecyl sulfonate and the like.Fluoroalkyl sulfonates are alkyl groups which bear 1 or more fluorineatoms and a sulfonate group. Fluoroalkyl sulfonates includetrifluoromethane sulfonate, perfluoroethyl sulfonate and the like.Likewise, an aryl sulfonate is an aryl group as defined herein whichbears a sulfonate group and optionally, one or more alkyl groups. Arylsulfonates thus include for example, benzene sulfonate, naphthalenesulfonate, dodecylbenzene sulfonate and cumene sulfonate.

A sulfone group has the chemical formula —S(O)₂R^(a) wherein R^(a) is aC₁₋₆ alkyl group. In some embodiments, R^(a) is a C₂₋₄ alkyl group

In one aspect, the present technology provides ionic liquids that bearpassivating functional groups. The functional groups allow the ionicliquid to passivate the surface of, e.g., carbon-based electrodes in anelectrochemical device during operation of the device. These new ionicliquids include a salt having a Formula selected from the groupconsisting of:

wherein R is selected from the group consisting of—CH₂Si(R″)₂[OSi(R″)₂]_(m)OSi(R″)₃, —(R′)—(OCH₂CH₂)_(n)—(OR″), a C₃₋₅cyclic carbonate, an oxalic borate group, a maleic anhydride group, asuccinic anhydride group, a sulfolane, and a C₁₋₆ alkyl groupsubstituted with a substituent selected from an isocyanate, sulfone,sulfolane, —OCO₂R″, C₃₋₅ cyclic carbonate, or oxalic borate group;

R′ is a C₁₋₄ alkylene group;

R″ is an alkyl group;

R₁, R₂, and R₃ are independently at each occurrence an alkyl, haloalkyl,alkyl substituted with carboxylate, aminoalkyl, cycloalkyl, aryl,heteroaryl, aralkyl, or heteroaralkyl group; or two of R₁, R₂, and R₃join together to form a C₄₋₅ alkylene group;R₄, R₅, R₆, R₇, and R₈ are independently at each occurrence H or analkyl, haloalkyl, hydroxyalkyl, cycloalkyl, aryl, heteroaryl, aralkyl,or heteroaralkyl group;X⁻ is an anion selected from the group consisting of borontetrafluoride, aluminate, (oxalate)borate, difluoro(oxalate)borate,phosphorus hexafluoride, alkylsulfonate, fluoroalkylsulfonate,arylsulfonate, bis(alkylsulfonyl)amide, perchlorate,bis(fluoroalkylsulfonyl)amide, bis(arylsulfonyl)amide, alkylfluorophosphate, (fluoroalkylsulfonyl)(fluoroalkylcarbonyl)amide,halide, nitrate, nitrite, sulfate, hydrogen sulfate, alkyl sulfate, arylsulfate, carbonate, bicarbonate, carboxylate, phosphate, hydrogenphosphate, dihydrogen phosphate, hypochlorite, an anionic site of acation-exchange resin, and a mixture of any two or more thereof;

n is an integer from 1 to 4; and

m is an integer from 0 to 10.

It will be understood that each dashed circle and plus sign in thechemical formulas represent a cationic aromatic system.

In some embodiments of the ionic liquid, the salt has the Formulaselected from the group consisting of:

In other embodiments, the salt has the Formula selected from the groupconsisting of:

In some embodiments of the ionic liquid, R is selected from the groupconsisting of —(R)(OCH₂CH₂)_(n)—(OR″),—CH₂Si(R″)₂[OSi(R″)₂]_(m)OSi(R″)₃, and a C₁₋₆ alkyl group substitutedwith a sulfone group. For example R may be —(CH₂)—(OCH₂CH₂)_(n)—(OCH₃),—CH₂Si(CH₃)₂-[OSi(CH₃)₂]_(m)OSi(CH₃)₃, or —(CH₂)—SO₂CH₃. In someembodiments, R″ is a C₁₋₄ alkyl group.

In some embodiments of the ionic liquid, R₁, R₂, and R₃. areindependently at each occurrence selected from the group consisting of aC₁₋₆ alkyl, hydroxyalkyl, and a haloalkyl group.

In some embodiments, R₄, R₅, R₆, R₇, and R₈ are independently at eachoccurrence a hydrogen or a C₁₋₆ alkyl group. In certain embodiments, R₄,R₅, and R₆ are each H.

In some embodiments the counterion, X⁻, of the ionic liquid is[CF₃CO₂]⁻; [C₂F₅CO₂]⁻; [ClO₄]⁻; [BF₄]⁻; [AsF₆]⁻; [PF₆]⁻; [PF₂(C₂O₄)₂]⁻;[PF₄C₂O₄]⁻; [CF₃SO₃]⁻; [N(CF₃SO₂)₂]⁻; [C(CF₃SO₂)₃]⁻; [N(SO₂C₂F₅)₂]⁻;alkyl fluorophosphate; [B(C₂O₄)₂]⁻; [BF₂C₂O₄]⁻; [B₁₂Y_(12-k)H_(k)]²⁻;[B₁₀Y_(10-k)H_(k′)]²⁻; or a mixture of any two or more thereof, whereinY is a halogen, k is an integer from 0 to 12 and k′ is an integer from 1to 10.

In some embodiments, the ionic liquid is a room temperature ionicliquid.

Exemplary ionic liquids include but are not limited to imidazolium saltswith oligo(ethylene glycol) groups such as:

-   1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide;-   1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-ium    bis(oxalato)borate;-   1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-ium    hexafluorophosphate,-   1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-ium    hexafluorophosphate, and-   3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-ium    hexafluorophosphate.

Further exemplary ionic liquids include but are not limited toimidazolium salts with siloxane groups such as:

-   1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide;-   1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-ium    hexafluorophosphate,-   1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-ium    hexafluorophosphate, and-   1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-ium    hexafluorophosphate.

Exemplary ionic liquids include but are not limited to imidazolium saltswith sulfone groups such as:

-   1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide;-   1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide;-   1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-ium    hexafluorophosphate,-   1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-ium    hexafluorophosphate,-   1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-ium    hexafluorophosphate, and-   1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-ium    hexafluorophosphate.

Exemplary ionic liquids include but are not limited to imidazolium saltswith carbonate groups such as:

-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-ium    bis(trifluoromethanesulfonyl)imide,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-ium    bis(oxalato)borate,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-ium    bis(fluoromethanesulfonyl)imide;-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-ium    hexafluorophosphate,-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-ium    hexafluorophosphate, and-   1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-ium    hexafluorophosphate.

Exemplary ionic liquids include but are not limited to phosphonium saltswith oligo(ethylene glycol) groups such as:

-   triethyl((2-methoxyethoxy)methyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl((2-(2-methoxyethoxyl)ethoxy)methyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl((2-(2-(2-methoxyethoxyl)ethoxy)ethoxy)methyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl((2-methoxyethoxy)methyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl((2-(2-methoxyethoxyl)ethoxy)methyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl((2-(2-(2-methoxyethoxyl)ethoxy)ethoxy)methyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl((2-methoxyethoxy)methyl)phosphonium bis(oxalato)borate,-   triethyl((2-(2-methoxyethoxyl)ethoxy)methyl)phosphonium    bis(oxalato)borate,-   triethyl((2-(2-(2-methoxyethoxyl)ethoxy)ethoxy)methyl)phosphonium    bis(oxalato)borate,-   triethyl((2-methoxyethoxy)methyl)phosphonium hexafluorophosphate,-   triethyl((2-(2-methoxyethoxyl)ethoxy)methyl)phosphonium    hexafluorophosphate, and-   triethyl((2-(2-(2-methoxyethoxyl)ethoxy)ethoxy)methyl)phosphonium    hexafluorophosphate.

Exemplary ionic liquids include but are not limited to phosphonium saltswith siloxane groups such as:

-   triethyl-(methylenepentamethyldisiloxane)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(methyleneheptamethyltrisiloxane)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(methyleneoctamethyltetrasiloxane)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(methylenepentamethyldisiloxane)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(methyleneheptamethyltrisiloxane)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(methyleneoctamethyltetrasiloxane)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(methylenepentamethyldisiloxane)phosphonium    bis(oxalato)borate,-   triethyl-(methyleneheptamethyltrisiloxane)phosphonium    bis(oxalato)borate,-   triethyl-(methyleneoctamethyltetrasiloxane)phosphonium    bis(oxalato)borate,-   triethyl-(methylenepentamethyldisiloxane)phosphonium    hexafluorophosphate,-   triethyl-(methyleneheptamethyltrisiloxane)phosphonium    hexafluorophosphate, and-   triethyl-(methyleneoctamethyltetrasiloxane)phosphonium    hexafluorophosphate.

Exemplary ionic liquids include but are not limited to phosphonium saltswith sulfone groups such as:

-   triethyl-(2-(methylsulfonyl)ethyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(2-(ethylsulfonyl)ethyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(2-(propylsulfonyl)ethyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(2-(butylsulfonyl)ethyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-(2-(methylsulfonyl)ethyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(2-(ethylsulfonyl)ethyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(2-(propylsulfonyl)ethyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(2-(butylsulfonyl)ethyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-(2-(methylsulfonyl)ethyl)phosphonium bis(oxalato)borate,-   triethyl-(2-(ethylsulfonyl)ethyl)phosphonium bis(oxalato)borate,-   triethyl-(2-(propylsulfonyl)ethyl)phosphonium bis(oxalato)borate,-   triethyl-(2-(butylsulfonyl)ethyl)phosphonium bis(oxalato)borate,-   triethyl-(2-(methylsulfonyl)ethyl)phosphonium hexafluorophosphate,-   triethyl-(2-(ethylsulfonyl)ethyl)phosphonium hexafluorophosphate,-   triethyl-(2-(propylsulfonyl)ethyl)phosphonium hexafluorophosphate,    and-   triethyl-(2-(butylsulfonyl)ethyl)phosphonium hexafluorophosphate.

Exemplary ionic liquids include but are not limited to phosphonium saltswith carbonate groups such as:

-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phosphonium    bis(trifluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phosphonium    bis(fluoromethylsulfonyl)imide,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phosphonium    bis(oxalato)borate,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phosphonium    bis(oxalato)borate,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phosphonium    bis(oxalato)borate,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phosphonium    hexafluorophosphate,-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phosphonium    hexafluorophosphate, and-   triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phosphonium    hexafluorophosphate.

In accordance with another aspect, there is provided an electrolyte foruse in an energy storage device, the electrolyte comprising a roomtemperature ionic liquid as described herein.

In some embodiments, the electrolyte includes a lithium salt in additionto the ionic liquid. A variety of lithium salts may be used includingfor example, Li[CF₃CO₂]; Li[C₂F₅CO₂]; Li[ClO₄]; Li[BF₄]; Li[AsF₆];Li[PF₆]; Li[PF₂(C₂O₄)₂]; Li[PF₄C₂O₄]; Li[CF₃SO₃]; Li[N(CF₃SO₂)₂];Li[C(CF₃SO₂)₃]; Li[N(SO₂C₂F₅)₂]; lithium alkyl fluorophosphates;Li[B(C₂O₄)₂]; Li[BF₂C₂O₄]; Li₂[B₁₂Z_(12-j)H_(j)];Li₂[B₁₀X_(10-j′)H_(j′)]; or a mixture of any two or more thereof,wherein Z is independently at each occurrence a halogen, j is an integerfrom 0 to 12 and j′ is an integer from 1 to 10.

In some embodiments, the concentration of the lithium salt present inthe ionic liquid ranges from about 0.01 M to about 1.5 M, from about0.05 M to about 1.2 M, or from about 0.4 M to about 1.0 M. If theconcentration of the ionic electrolyte salt is less than about 0.01 M,the ionic conductivity of the resulting non-aqueous electrolyte tends todecrease due to an inadequate number of carrier ions in the electrolyte.

In some applications of the present electrolyte, such as a formulationfor a lithium ion battery, aprotic solvents are combined with thepresent ionic liquids to decrease the viscosity and increase theconductivity. Aprotic solvents lack exchangeable protons and includecyclic carbonic acid esters, linear carbonic acid esters, phosphoricacid esters, oligoether substituted siloxanes/silanes, cyclic ethers,chain ethers, lactone compounds, chain esters, nitrile compounds, amidecompounds, sulfone compounds and the like. These solvents may be usedsingly, or at least two of them in admixture. Examples of aproticsolvents or carriers for forming the electrolyte systems include but arenot limited to dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropylcarbonate, bis(trifluoroethyl)carbonate,bis(pentafluoropropyl)carbonate, trifluoroethyl methyl carbonate,pentafluoroethyl methyl carbonate, heptafluoropropyl methyl carbonate,perfluorobutyl methyl carbonate, trifluoroethyl ethyl carbonate,pentafluoroethyl ethyl carbonate, heptafluoropropyl ethyl carbonate,perfluorobutyl ethyl carbonate, etc., fluorinated oligomers,dimethoxyethane, triglyme, dimethylvinylene carbonate,tetraethyleneglycol, dimethyl ether, polyethylene glycols, sulfones, andgamma-butyrolactone.

In some embodiments, the inventive electrolytes further include anelectrode stabilizing additive to protect the electrodes fromdegradation. Thus, electrolytes of the present technology can include anelectrode stabilizing additive that can be reduced or polymerized on thesurface of a negative electrode to form a passivation film on thesurface of the negative electrode. Likewise, inventive electrolytes caninclude an electrode stabilizing additive that can be oxidized orpolymerized on the surface of the positive electrode to form apassivation film on the surface of the positive electrode. In someembodiments, electrolytes of the present technology further includemixtures of the two types of electrode stabilizing additives. Theadditives are typically present at a concentration of about 0.001 to 8wt %.

In some embodiments, an electrode stabilizing additive is a substitutedor unsubstituted linear, branched or cyclic hydrocarbon comprising atleast one oxygen atom and at least one aryl, alkenyl or alkynyl group.The passivating film formed from such electrode stabilizing additivesmay also be formed from a substituted aryl compound or a substituted orunsubstituted heteroaryl compound where the additive comprises at leastone oxygen atom. Alternatively, a combination of two additives may beused. In some such embodiments, one additive is selective for forming apassivating film on the cathode to prevent leaching of metal ions andthe other additive can be selective for passivating the anode surface toprevent or lessen the reduction of metal ions at the anode.

Representative electrode stabilizing additives include 1,2-divinylfuroate, 1,3-butadiene carbonate, 1-vinylazetidin-2-one,1-vinylaziridin-2-one, 1-vinylpiperidin-2-one, 1 vinylpyrrolidin-2-one,2,4-divinyl-1,3-dioxane, 2 amino-3 vinylcyclohexanone,2-amino-3-vinylcyclopropanone, 2 amino-4-vinylcyclobutanone,2-amino-5-vinylcyclopentanone, 2-aryloxy-cyclopropanone,2-vinyl-[1,2]oxazetidine, 2 vinylaminocyclohexanol,2-vinylaminocyclopropanone, 2 vinyloxetane, 2-vinyloxy-cyclopropanone,3-(N-vinylamino)cyclohexanone, 3,5-divinyl furoate,3-vinylazetidin-2-one, 3 vinylaziridin 2 one, 3 vinylcyclobutanone, 3vinylcyclopentanone, 3 vinyloxaziridine, 3 vinyloxetane,3-vinylpyrrolidin-2-one, 4,4 divinyl-3 dioxolan 2-one, 4vinyltetrahydropyran, 5-vinylpiperidin-3-one, allylglycidyl ether,butadiene monoxide, butyl vinyl ether, dihydropyran-3-one, divinyl butylcarbonate, divinyl carbonate, divinyl crotonate, divinyl ether, divinylethylene carbonate, divinyl ethylene silicate, divinyl ethylene sulfate,divinyl ethylene sulfite, divinyl methoxypyrazine, divinylmethylphosphate, divinyl propylene carbonate, ethyl phosphate,methoxy-o-terphenyl, methyl phosphate, oxetan-2-yl-vinylamine,oxiranylvinylamine, vinyl carbonate, vinyl crotonate, vinylcyclopentanone, vinyl ethyl-2-furoate, vinyl ethylene carbonate, vinylethylene silicate, vinyl ethylene sulfate, vinyl ethylene sulfite, vinylmethacrylate, vinyl phosphate, vinyl-2-furoate, vinylcylopropanone,vinylethylene oxide, β-vinyl-γ-butyrolactone, or a mixture of any two ormore thereof. In some embodiments the electrode stabilizing additive maybe a cyclotriphosphazene that is substituted with F, alkyloxy,alkenyloxy, aryloxy, methoxy, allyloxy groups, or combinations thereof.For example, the additive may be a(divinyl)-(methoxy)(trifluoro)cyclotriphosphazene,(trivinyl)(difluoro)(methoxy)cyclotriphosphazene,(vinyl)(methoxy)(tetrafluoro)cyclotriphosphazene,(aryloxy)(tetrafluoro)(methoxy)-cyclotriphosphazene,(diaryloxy)(trifluoro)(methoxy)cyclotriphosphazene compounds, or amixture of two or more such compounds. In some embodiments, theelectrode stabilizing additive is vinyl ethylene carbonate, vinylcarbonate, or 1,2-diphenyl ether, or a mixture of any two or more suchcompounds.

Other representative electrode stabilizing additives may includecompounds with phenyl, naphthyl, anthracenyl, pyrrolyl, oxazolyl,furanyl, indolyl, carbazolyl, imidazolyl, or thiophenyl groups. Forexample, electrode stabilizing additives may be aryloxpyrrole, aryloxyethylene sulfate, aryloxy pyrazine, aryloxy-carbazole trivinylphosphate,aryloxy-ethyl-2-furoate, aryloxy-o-terphenyl, aryloxy-pyridazine,butyl-aryloxy-ether, divinyl diphenyl ether,(tetrahydrofuran-2-yl)-vinylamine, divinyl methoxybipyridine,methoxy-4-vinylbiphenyl, vinyl methoxy carbazole, vinyl methoxypiperidine, vinyl methoxypyrazine, vinyl methyl carbonate-allylanisole,vinyl pyridazine, 1-divinylimidazole, 3-vinyltetrahydrofuran, divinylfuran, divinyl methoxy furan, divinylpyrazine, vinyl methoxy imidazole,vinylmethoxy pyrrole, vinyl-tetrahydrofuran, 2,4-divinyl isooxazole, 3,4divinyl-1-methyl pyrrole, aryloxyoxetane, aryloxy-phenyl carbonate,aryloxy-piperidine, aryloxy-tetrahydrofuran, 2-aryl-cyclopropanone,2-diaryloxy-furoate, 4-allylanisole, aryloxy-carbazole,aryloxy-2-furoate, aryloxy-crotonate, aryloxy-cyclobutane,aryloxy-cyclopentanone, aryloxy-cyclopropanone,aryloxy-cycolophosphazene, aryloxy-ethylene silicate, aryloxy-ethylenesulfate, aryloxy-ethylene sulfite, aryloxy-imidazole,aryloxy-methacrylate, aryloxy-phosphate, aryloxy-pyrrole,aryloxyquinoline, diaryloxycyclotriphosphazene, diaryloxy ethylenecarbonate, diaryloxy furan, diaryloxy methyl phosphate, diaryloxy-butylcarbonate, diaryloxy-crotonate, diaryloxy-diphenyl ether,diaryloxy-ethyl silicate, diaryloxy-ethylene silicate,diaryloxy-ethylene sulfate, diaryloxyethylene sulfite, diaryloxy-phenylcarbonate, diaryloxy-propylene carbonate, diphenyl carbonate, diphenyldiaryloxy silicate, diphenyl divinyl silicate, diphenyl ether, diphenylsilicate, divinyl methoxydiphenyl ether, divinyl phenyl carbonate,methoxycarbazole, or 2,4-dimethyl-6-hydroxy-pyrimidine, vinylmethoxyquinoline, pyridazine, vinyl pyridazine, quinoline, vinylquinoline, pyridine, vinyl pyridine, indole, vinyl indole,triethanolamine, 1,3-dimethyl butadiene, butadiene, vinyl ethylenecarbonate, vinyl carbonate, imidazole, vinyl imidazole, piperidine,vinyl piperidine, pyrimidine, vinyl pyrimidine, pyrazine, vinylpyrazine, isoquinoline, vinyl isoquinoline, quinoxaline, vinylquinoxaline, biphenyl, 1,2-diphenyl ether, 1,2-diphenylethane, oterphenyl, N-methyl pyrrole, naphthalene, or a mixture of any two ormore such compounds.

In some other embodiments, the electrolyte of the present technologyincludes an aprotic gel polymer carrier/solvent. Suitable gel polymercarrier/solvents include polyethers, polyethylene oxides, polyimides,polyphosphazines, polyacrylonitriles, polysiloxanes, polyether graftedpolysiloxanes, derivatives of the foregoing, copolymers of theforegoing, cross-linked and network structures of the foregoing, blendsof the foregoing, and the like, to which is added a suitable ionicelectrolyte salt. Other gel-polymer carrier/solvents include thoseprepared from polymer matrices derived from polypropylene oxides,polysiloxanes, sulfonated polyimides, perfluorinated membranes (Nafionresins), divinyl polyethylene glycols, polyethylene glycol-bis-(methylacrylates), polyethylene glycol-bis(methyl methacrylates), derivativesof the foregoing, copolymers of the foregoing, cross-linked and networkstructures of the foregoing.

The inventive functional ionic liquids and the electrolytic solutioncontaining the salt are high in electrical conductivity and solubilityin organic solvents, and are suitable for use as an electrolyticsolution for electrochemical devices. Examples of electrochemicaldevices are electric double-layer capacitor, secondary batteries, solarcells of the pigment sensitizer type, electrochromic devices, condenser,etc., which are nevertheless not limitative. Especially suitable aselectrochemical devices are electric double-layer capacitor andsecondary batteries such as lithium ion battery.

In yet another aspect, an electrochemical device is provided thatincludes a cathode; an anode; and an electrolyte including an ionicliquid as described herein. In one embodiment, the electrochemicaldevice is a lithium secondary battery. In some embodiments, thesecondary battery is a lithium battery, a lithium-ion battery, alithium-sulfur battery, a lithium-air battery, a sodium ion battery, ora magnesium battery. In some embodiments, the electrochemical device isan electrochemical cell such as a capacitor. In some embodiments, thecapacitor is an asymmetric capacitor or supercapacitor. In someembodiments, the electrochemical cell is a primary cell. In someembodiments, the primary cell that is a lithium/MnO₂ battery orLi/poly(carbon monofluoride) battery. In some embodiments, theelectrochemical cell is a solar cell.

Suitable cathodes include those such as, but not limited to, a lithiummetal oxide, spinel, olivine, carbon-coated olivine, LiFePO₄, LiCoO₂,LiNiO₂, LiNi_(1−x)Co_(y)Met_(z)O₂, LiMn_(0.5)Ni_(0.5)O₂,LiMn_(0.3)Co_(0.3)Ni_(0.3)O₂, LiMn₂O₄, LiFeO₂,Li_(1+x′)Ni_(α)Mn_(β)Co_(γ)Met′_(δ)O_(2−z′)F_(z′), A_(n′)B₂(XO₄)₃(NASICON), vanadium oxide, lithium peroxide, sulfur, polysulfide, alithium carbon monofluoride (also known as LiCFx), or mixtures of anytwo or more thereof, where Met is Al, Mg, Ti, B, Ga, Si, Mn, or Co; Met′is Mg, Zn, Al, Ga, B, Zr, or Ti; A is Li, Ag, Cu, Na, Mn, Fe, Co, Ni,Cu, or Zn; B is Ti, V, Cr, Fe, or Zr; X is P, S, Si, W, or Mo; 0≦x≦0.3,0≦y≦0.5, 0≦z≦0.5; 0≦x′≦0.4, 0≦α≦1, 0≦β≦1, 0≦γ≦1, 0≦δ≦0.4, and 0≦z′≦0.4;and 0≦n′≦3. According to some embodiments, the spinel is a spinelmanganese oxide with the formula ofLi_(1+x)Mn_(2−z)Met′″_(y)O_(4−m)X′_(n), wherein Met′″ is Al, Mg, Ti, B,Ga, Si, Ni, or Co; X′ is S or F; and wherein 0≦x≦0.3, 0≦y≦0.5, 0≦z≦0.5,0≦m≦0.5 and 0≦n≦0.5. In other embodiments, the olivine has a formula ofLi_(1+x)Fe_(1−z)Met″_(y)PO_(4−m)X′_(n), wherein Met″ is Al, Mg, Ti, B,Ga, Si, Ni, Mn or Co; X′ is S or F; and wherein 0≦x≦0.3, 0≦y≦0.5,0≦z≦0.5, 0≦m≦0.5 and 0≦n≦0.5.

Suitable anodes include those such as lithium metal; graphiticmaterials, amorphous carbon, Li₄Ti₅O₁₂, tin alloys, silicon alloys,intermetallic compounds, or mixtures of any two or more such materials.Suitable graphitic materials including natural graphite, artificialgraphite, graphitized meso-carbon microbeads (MCMB), and graphitefibers, as well as any amorphous carbon materials. In some embodiments,the anode and cathode are separated from each other by a porousseparator.

The separator for the lithium battery often is a microporous polymerfilm. Examples of polymers for forming films include: nylon, cellulose,nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride,polypropylene, polyethylene, polybutene, or copolymers or blends of anytwo or more such polymers. In some instances, the separator is anelectron beam treated micro-porous polyolefin separator. The electrontreatment can improve the deformation temperature of the separator andcan accordingly enhance the high temperature performance of theseparator. Additionally, or alternatively, the separator can be ashut-down separator. The shut-down separator can have a triggertemperature above 130° C. to permit the electrochemical cells to operateat temperatures up to 130° C.

One skilled in the art will readily realize that all ranges discussedcan and do necessarily also describe all subranges therein for allpurposes and that all such subranges also form part and parcel of thispresent technology. Any listed range can be easily recognized assufficiently describing and enabling the same range being broken downinto at least equal halves, thirds, quarters, fifths, tenths, etc. As anon-limiting example, each range discussed herein can be readily brokendown into a lower third, middle third and upper third, etc.

All publications, patent applications, issued patents, and otherdocuments referred to in this specification are herein incorporated byreference as if each individual publication, patent application, issuedpatent, or other document was specifically and individually indicated tobe incorporated by reference in its entirety. Definitions that arecontained in text incorporated by reference are excluded to the extentthat they contradict definitions in this disclosure.

The present technology, thus generally described, will be understoodmore readily by reference to the following examples, which are providedby way of illustration and are not intended to be limiting of thepresent technology.

EXAMPLES

Ionic liquids of the present technology may be synthesized by variousmethods known in the art. For example, to prepare cationic phosphonium,imidazolium, pyridinium, or quaternary ammonium-based ionic liquids, thecorresponding phosphite, 1-substituted imidazole, pyridine, or tertiaryamine may be reacted with a suitable electrophile under alkylatingconditions and then reacted with a suitable lithium salt (i.e., LiXwhere X is defined as herein). Suitable electrophiles include R groups(as defined herein) bearing, e.g., a halide, mesylate, triflate orsimilar leaving group. By way of non-limiting example, Scheme 1 showsthe synthesis of representative ionic liquids of the present technology.Preparation of oxazolium and thizolium-based ionic liquids is similar,but requires deprotonation of the corresponding oxazole or thiazole withan appropriate base, e.g., an alkali metal hydride prior to reactionwith the electrophile.

Example 1 Synthesis of IL1-I

A mixture consisting of equimolar quantities of triethylphosphine (20 g,0.17 mmol) and ICH₂SiMe₂OSiMe₃ (48 g, 0.17 mmol) was stirred at roomtemperature for 24 h. The resulting solid was washed three times withhexane then diethyl ether and placed under vacuum to afford IL1-I.Yield: 49 g (72%). ¹H NMR (CDCl₃) is shown in FIG. 1.

Example 2 Synthesis of IL1-TFSI

A solution of IL1-I (48.8 g, 0.16 mol) in water (300 mL) was treatedwith lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (44.6 g, 0.17mol). The solution was allowed to stir at room temperature for a periodof 12 h at which time the room temperature ionic liquid IL1-TFSI formeda second layer at the bottom of the flask. IL1-TFSI was dissolved inCH₂Cl₂, and washed with deionized water until no residual I⁻ in therinse can be detected by 0.1 M AgNO₃ solution. The CH₂Cl₂ was stirredwith carbon black and Al₂O₃ for 2 h and filtered. The crude product wasdried under high vacuum (0.02 torr) at 100° C. for 16 h. Yield: 50 g(75%). ¹H NMR (CDCl₃) is shown in FIG. 1

Example 3 Synthesis of IL2-I

Freshly distilled ICH₂SiMe₂OSiMe₃ (48.7 g, 0.16 mol) was added in oneportion to a 500 mL thick walled glass reactor containing 1-methylimidazole (13.9 g, 0.16 mol) equipped with a magnetic stirrer and awater cooled condenser. The solution was stirred for 16 h at 100° C. Thesolution was cooled down to room temperature and stirred with hexane.The precipitate was filtered and washed several times with hexane anddiethyl ether, dried overnight under vacuum. Yield for IL2-I: 60.5 g(95%). ¹H NMR (CDCl₃) is shown in FIG. 2.

Example 4 Synthesis of IL2-TFSI

A solution of lithium bis(trifluoromethanesulfonyl)imide (46.4 g, 0.16mol) in 100 mL of H₂O was added dropwise to a solution of IL2-I (59.8 g,0.16 mol) in 150 mL of H₂O. The solution was stirred at ambienttemperature for 12 h. Dichloromethane (250 mL) was added, and themixture was transferred to a separatory funnel. The lower phase (ionicliquid+CH₂Cl₂) was collected. The ionic liquid was purified through ashort alumina column, and the CH₂Cl₂ removed on a rotary evaporator. Theresultant hydrophobic liquid was washed three times with 150 mL of H₂Oand dried for 12 h at 100° C. under vacuum to afford IL2-TFSI (69 g, 80%yield) as a pale yellow liquid. ¹H NMR (CDCl₃) is shown in FIG. 2

Example 5 Synthesis of IL3-Br

BrCH₂CH₂SO₂Me (14.3 g, 0.076 mol) was added in one portion to a 250 mLround bottom flask containing 1-methyl imidazole (6.3 g, 0.076 mol)equipped with a magnetic stirrer and a water cooled condenser. Thesolution was stirred for 16 h at 100° C. The oil residue was treatedwith CH₃CN to precipitate the product. The precipitate was filtered andwashed several times with pre-cooled CH₃CN, dried overnight undervacuum. Yield for IL2-I: 12.4 g (60%). ¹H NMR (DMSO d₆) is shown in FIG.3.

Example 6 Synthesis of IL3-TFSI

A solution of lithium bis(trifluoromethanesulfonyl)imide (13.2 g, 0.046mol) in 60 mL of H₂O was added dropwise to a solution of IL2-I (12.4 g,0.046 mol) in 100 mL of H₂O. The solution was stirred at ambienttemperature for 12 h. Methylene dichloride (500 mL) was added, and allwas transferred to a separatory funnel. The lower phase (ionicliquid+CH₂Cl₂) was collected. Ionic liquid was purified through a shortalumina column, and the CH₂Cl₂ removed on a rotary evaporator. Theresultant hydrophobic liquid was washed three times with 150 mL of H₂Oand dried for 12 h at 100° C. under vacuum to afford IL3-TFSI (10.2 g,53% yield) as a colorless liquid. ¹H NMR (CD₃CN) is shown in FIG. 3.

Example 7 Comparative Example, Li/MCMB Half Cell Charge DischargeProfiles

Li/MCMB half cell charge discharge profiles were measured using 0.8MLiTFSI in conventional tetraethylphosphoniumbis(trifluoromethanesulfonyl)imide ionic liquid. See FIG. 4. Thecharging curve showed that no regular intercalation of Li was observed.Instead, it showed a plateau at higher potential at 0.5V vs Li′/Liindicating ionic liquid co-intercalation/reduction reaction on the MCMBelectrode.

Example 8 Li/MCMB Half Cell Charge Discharge Profiles, FIG. 5

Li/MCMB half cell charge discharge profiles using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI). The 1^(st) cycle chargingcurve showed that a solid electrolyte interphase formation (SEI)starting at 0.8V. The 2^(nd) cycle and subsequent cycles are showedregular lithium interaction and de-intercalation on the MCMB electrode.This is a good example that introduction of some functional ionic liquid(Si—O—Si unit in this case) has SEI formation capability and the new ILis completely compatible with graphite based material.

Example 9 dQdV Profile of Li/MCMB Half Cell, FIG. 6

dQdV profile of Li/MCMB half cell using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI). dQdV curves clearly showsthe reduction of the functional ionic liquid passiviating the surface ofthe graphite electrode. This self SEI formation capability can provide aeasy solution to address the issue of IL compatibility with graphiteelectrode.

Example 10 Comparative Example, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li HalfCell Charge Discharge Profile, FIG. 7

LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li half cell charge discharge cyclingperformance using conventional 0.8M LiTFSI in tetraethylphosphoniumbis(trifluoromethanesulfonyl)imide ionic liquid. The conventional IL cannot provide high efficiency in the cycling test of the positive halfcell.

Example 11 LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li Half Cell Charge DischargeProfile, FIG. 8

LiNi_(0.8)Co_(0.15)Al_(0.05)O₂/Li half cell charge discharge cyclingperformance using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI) at 55° C. The inventivefunctional ionic liquid can provide excellent compatibility with lithiumoxide cathode material, which is impossible for the conventional IL asindicated in FIG. 7.

Example 12 FIG. 9

MCMB/Li half cell charge discharge cycling performance usingconventional 0.8M LiTFSI in tetraethylphosphoniumbis(trifluoromethanesulfonyl)imide ionic liquid. Using conventionalionic liquid, the capacity of the MCMB half cell dramatically decreaseswith cycle number.

Example 13 Li/MCMB Half Cell Charge Discharge Profiles, FIG. 10

MCMB/Li half cell charge discharge cycling performance using 0.8M LiTFSIin triethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)-imide (IL1-TFSI). The functionalized ionicliquid showed reversible charge/discharge performance.

Example 14 MCMB/LiNi_(0.80)Ni_(0.15)Al_(0.05)O₂ Full Cell ChargeDischarge Profiles, FIG. 11

MCMB/LiNi_(0.80)Ni_(0.15)Al_(0.05)O₂ full cell charge discharge cyclingperformance using conventional 0.8M LiTFSI in tetraethylphosphoniumbis(trifluoromethanesulfonyl)imide ionic liquid. Poor capacity retentionwas observed for the conventional ionic liquid in a full lithium ioncell.

Example 15 MCMB/LiNi_(0.85)Ni_(0.15)Al_(0.05)O₂, Full Cell ChargeDischarge Profiles, FIG. 12

MCMB/LiNi_(0.85)Co_(0.15)Al_(0.05)O₂ full cell charge discharge cyclingperformance using 0.8M LiTFSI intriethyl-(methylenepentamethyldisiloxane)phosphoniumbis(trifluoromethylsulfonyl)imide (IL1-TFSI). Much improved cyclingperformance was achieved by using the functionalized ionic liquidIL1-TFSI.

What is claimed is:
 1. An electrochemical device comprising: a cathode;an anode; and an electrolyte comprising an ionic liquid represented as:

wherein: R is selected from the group consisting of—CH₂Si(R″)₂[OSi(R″)₂]_(m)O—Si(R″)₃, —(R′)—(OCH₂CH₂)_(n)—(OR″), a C₃-C₅cyclic carbonate, a sulfolane, an oxalic borate group, a maleicanhydride group, a succinic anhydride group, and a C₁-C₆ alkyl groupsubstituted with a substituent selected from an isocyanate, sulfone,sulfolane, —OCO₂R″, C₃-C₅ cyclic carbonate, or oxalic borate group; R′is a C₁₋₄ alkylene group; R″ is an alkyl group; R₁, R₂, and R₃ areindependently at each occurrence alkyl, cycloalkyl, aryl, heteroaryl,aralkyl, or heteroaralkyl, or any two of R₁, R₂, and R₃ join together toform a C₄-C₅ cycloalkylene group; R₄, R₅, and R₆ are independently ateach occurrence H, alkyl, cycloalkyl, aryl, heteroaryl, aralkyl, orheteroaralkyl; each X⁻ independently comprises boron tetrafluoride,aluminate, bis(oxalato)borate, difluoro(oxalate)borate, phosphorushexafluoride, alkyl sulfonate, fluoroalkyl sulfonate, aryl sulfonate,bis(alkylsulfonyl)amide, perchlorate, bis(fluoroalkylsulfonyl)amide,bis(arylsulfonyl)amide, alkyl fluorophosphate,(fluoroalkylsulfonyl)(fluoroalkylcarbonyl)amide, halide, nitrate,nitrite, sulfate, hydrogen sulfate, alkyl sulfate, aryl sulfate,carbonate, bicarbonate, perfluoroalkyl group substituted withcarboxylate, phosphate, hydrogen phosphate, dihydrogen phosphate,hypochlorite, an anionic site of a cation-exchange resin, or a mixtureof any two or more thereof; n is an integer from 1 to 4; and m is aninteger from 0 to
 10. 2. The electrochemical device of claim 1 that is alithium secondary battery.
 3. The electrochemical device of claim 2wherein the secondary battery is a lithium battery, a lithium-ionbattery, a lithium-sulfur battery, a lithium-air battery, a sodium ionbattery, or a magnesium battery.
 4. The electrochemical device of claim1, wherein each R is independently (R′)—(OCH₂CH₂)_(n)—(OR″),—CH₂Si(R″)₂[OSi(R″)₂]_(m)OSi(R″)₃, or a C₁₋₆ alkyl group substitutedwith a sulfone group.
 5. The electrochemical device of claim 1, whereinR₁, R₂, and R₃ are independently at each occurrence C₁-C₆ alkyl,hydroxyalkyl, or haloalkyl group.
 6. The electrochemical device of claim1, wherein R₁ is a C₂-C₆ alkyl.
 7. The electrochemical device of claim1, wherein R₄, R₅, and R₆ are each H.
 8. The electrochemical device ofclaim 1, wherein X⁻ is [CF₃CO₂]⁻; [C₂F₅CO₂]⁻; [ClO₄]⁻; [BF₄]⁻; [AsF₆]⁻;[PF₆]⁻; [PF₂(C₂O₄)₂]⁻; [PF₄C₂O₄]⁻; [CF₃SO₃]⁻; [N(CF₃SO₂)₂]⁻;[C(CF₃SO₂)₃]⁻; [N(SO₂C₂F₅)₂]⁻; an alkyl fluorophosphate; [B(C₂O₄)₂]⁻;[BF₂C₂O₄]⁻; [B₁₂Y_(12-k)H_(k)]²⁻; [B₁₀Y_(10-k′)H_(k′)]²⁻; or a mixtureof any two or more thereof, wherein Y is independently at eachoccurrence a halogen, k is an integer from 0 to 12, and k′ is an integerfrom 1 to
 10. 9. The electrochemical device of claim 1, wherein theionic liquid has the Formula:


10. The electrochemical device of claim 9, wherein R is—(CH₂)—(OCH₂CH₂)_(n)—(OCH₃), —CH₂Si(CH₃)₂[OSi(CH₃)₂]_(m)OSi(CH₃)₃, or—(CH₂)_(n)SO₂CH₃.
 11. The electrochemical device of claim 1, wherein theionic liquid has the Formula:


12. The electrochemical device of claim 11, wherein R is wherein R is—(CH₂)—(OCH₂CH₂)_(n)—(OCH₃), —CH₂Si(CH₃)₂[OSi(CH₃)₂]_(m)OSi(CH₃)₃, or—(CH₂)_(n)SO₂CH₃.
 13. The electrochemical device of claim 12, wherein R₁is a C₂-C₆ alkyl.
 14. The electrochemical device of claim 1, wherein mis 1, 2, 3, 4, 5, 6, 7, 8, 9, or
 10. 15. The electrochemical device ofclaim 1, wherein the ionic liquid comprises:1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-iumbis(oxalato)borate; 3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-((2-methoxyethoxy)methyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-((2-(2-methoxyethoxyl)ethoxy)methyl)-1H-imidazol-3-iumhexafluorophosphate;3-2,5,8,11-tetraoxadodecyl-1-ethyl-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(methylenepentamethyldisiloxane)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(methyleneheptamethyltrisiloxane)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(methyleneoctamethyltetrasiloxane)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-iumbis(oxalato)borate; 1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-iumbis(oxalato)borate; 1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-(2-(methylsulfonyl)ethyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(2-(propylsulfonyl)ethyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-(2-(butylsulfonyl)ethyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-iumbis(trifluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-iumbis(oxalato)borate;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-iumbis(fluoromethanesulfonyl)imide;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)methyl)-1H-imidazol-3-iumhexafluorophosphate;1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)ethyl)-1H-imidazol-3-iumhexafluorophosphate; or1-ethyl-3-((2-oxo-1,3-dioxolan-4-yl)propyl)-1H-imidazol-3-iumhexafluorophosphate.
 16. The electrochemical device of claim 1, whereinthe electrolyte further comprises a lithium salt.
 17. Theelectrochemical device of claim 1, wherein a concentration of thelithium salt in the ionic liquid is from about 0.01 M to about 1.5 M.18. The electrochemical device of claim 1, wherein the electrolytefurther comprises an aprotic solvent.
 19. The electrochemical device ofclaim 1, wherein the electrolyte further comprises an aprotic gelpolymer carrier/solvent.
 20. The electrochemical device of claim 1,wherein the electrolyte further comprises an electrode stabilizingadditive.